Components that are subjected to wear, such as abrasion resistant components in mining applications, are typically provided with a layer of wear resistant material. In certain cases the entire component may be manufactured in a wear resistant material.
Plasma transferred arc welding (PTAW) is a conventional method for manufacturing of wear resistant coatings on products. In PTAW, a powder mixture of hard tungsten carbide particles and ductile metal powder is fed through a nozzle into a plasma, in which the powder is fused so that the solid tungsten carbide particles are suspended in molten metal powder. The fused powder is transferred onto the surface of the steel component where it solidifies into a wear resistant layer that comprises hard tungsten carbide particles in a matrix of a relatively ductile metal binder phase. In wear resistant layers, the volume ratio of the hard and ductile phases as well as their distribution is very important for the performance and overall life length of the wear resistant layer.
However, wear resistant layers that have been applied by PTAW suffer from several drawbacks. For instance, during solidifying of wear resistant layers applied by PTAW, the alloy elements segregate in the molten metal matrix and cause inclusions of e.g. borides and carbides to grow rapidly into large blocks or elongated needle like shapes. As the inclusions grow, they connect with each other and form brittle networks in the ductile metal phase between adjacent tungsten carbide particles, hence reducing the ductility of the wear resistant layer. FIG. 9 shows a SEM image of a portion of conventional PTAW applied material. In the image, networks of interconnected needle- and block shaped borides and carbides are visible in the matrix between the large white tungsten particles.
Also, due to differences in density between tungsten carbide and the metal alloy of the binder phase, the tungsten carbides tend to sink towards the bottom of the applied wear resistant layer. This causes a lower concentration of hard particles in the surface region of the wear resistant layer, thus reducing the hardness of the wear resistant layer. FIG. 8 shows a portion of conventional PTAW applied material in which the surface zone has few tungsten carbide.
It is further difficult to manufacture thick wear resistant layers with PTAW since thermal stress is created in the layers during solidifying. Furthermore, it is difficult to use PTAW for applying wear resistant layers to components of complicated shapes.
Hence, it is an object of the present invention to solve at least one of the above mentioned problems. In particular, it is an object of the present invention to achieve a method which allows for manufacturing components with improved wear resistance. A further object of the present invention is to achieve a component which has high wear resistance. Yet a further object of the present invention is to provide a powder mixture which allows manufacturing of components with high wear resistance.